The present invention relates generally to an apparatus for detecting combustion flame light in an internal combustion engine and more particularly to a sensor for detecting the air-fuel ratio of combustion gas mixture on the basis of spectral characteristics of the combustion light.
Various approaches have heretofore been made to extract externally the combustion flame light signal produced within the engine for utilizing as information concerning the combustion. By way of example, optical ignition timing detection system is actually adopted in diesel engines and others.
On the other hand, there is disclosed in JP-A-No. 58-82039 a system for determining the air-fuel ratio by detecting light intensities emitted by combustion within the engine and by making use of the intensity ratios. However, in this prior known system, no appropriate measures are adopted for coping with the changes in transmittivity of a combustion light detecting element face due to dirt or contamination. Consequently, difficulty is encountered in detecting the air-fuel ratio with a satisfactorily high accuracy.
More specifically, the hitherto known air-fuel ratio detecting system is operative on the basis of the ratio of intensities of combustion flame light having particular wavelengths suffers from various shortcomings such as change in the transmittivity of the distinct light wavelengths due to deposition on the detecting end face, variation in the intensity ratio brought about by heat radiation under high environmental temperature condition, whereby the detection of air-fuel ratio with satisfactorily high accuracy is rendered essentially impractical.